Aims and Objectives: This study explores Spanish heritage speakers’ (HSs) knowledge of clitic climbing and the (extra-)linguistic factors that modulate it. Design: Heritage speakers of Spanish completed three screening tasks (a background language questionnaire, a productive vocabulary task, and proficiency task) and two experimental tasks (an elicited production task, and a forced choice task) examining their knowledge of clitic climbing in different contexts. Data and Analysis: Thirty-nine participants completed two experimental tasks. Each task included 32 critical items distributed in four conditions. The data were analyzed using generalized linear mixed models. Findings: Patterns of language exposure and use are a strong predictor for clitic climbing knowledge while the effects of age of onset of bilingualism found contradict our hypothesis. Originality: This study examines production and interpretation data of clitic climbing knowledge in combination with extralinguistic factors that may facilitate heritage language acquisition and maintenance. Sequential bilinguals show a stronger enclisis bias than simultaneous bilinguals. Significance: The results show that, in cases of optionality, self-reported heritage language exposure and use may be a stronger predictor than age of onset of bilingualism of the dominant language. Limitations: This study does not have acceptability data on either grammatical or ungrammatical instances of proclisis or enclisis. In addition, because the test items feature different verbs, no lexical analysis can be conducted. Finally, using an adapted version of the BLP instead of its original normed version restricts opportunities for comparability and reproducibility.